Technical Abstract:
Cellulose acetate has been widely used in UV-B enhancement studies under field and controlled-environment conditions since the early 1970's to remove wavelengths below ca. 290 nm, without any evidence of toxicity effects. However, in the course of conducting UV-B exclusion studies in window boxes covered with cellulose acetate (CA), or in Plexiglas chambers lined with CA, marginal chlorosis and cotyledon epinasty were observed in "Ashley" cucumber, while seedlings exposed to open sunlight and those grown under polyester (PE) film to exclude UV-B, were free of visible injury. These findings suggest that the CA filter itself may be causing toxicity. To test this hypothesis, an UV exclusion study was conducted in which CA or Teflon (T), both UV-B and UV-A transmitting films, were used to cover window boxes in the following four combinations (top/bottom): CA/CA; CA/T; T/CA; and T/T. When CA was used as the bottom filter (CA/CA and T/CA), the eplants showed significantly greater leaf injury and a 2-3 fold reduction i growth than when T was used as the bottom filter (CA/T and T/T). These findings suggest that toxicity is caused by CA itself, rather than by solar UV-B radiation, possibly as a result of outgassing of phthalates, known to be used as plasticizers in the manufacture of CA. Further evidence that CA was responsible for leaf injury, rather than UV-B, was provided by a companion study in which T was replaced by PE and damage was still observed, although no significant growth effects of CA position were observed.